What is the significance of the axis in a prescription?

The axis in a prescription is essential because it indicates the orientation of astigmatism correction. Astigmatism is caused by an irregular shape of the cornea or lens, which results in different refractive powers in different meridians of the eye. The axis value is measured in degrees and denotes where along the 360-degree plane the cylindrical power for correcting astigmatism should be applied.

For example, if a lens is prescribed with a specific cylinder power to correct astigmatism, the axis tells the optician or technician how to position the lens correctly on the patient's eye. Without the correct axis, the cylindrical power would not effectively correct the patient's vision, resulting in inadequate treatment of their astigmatism.